Despite its many limitations PDSI is still a meaningful indicator of short term climate variability (interannual, maybe up to decadal, time scales). If you look at the uncertainties described by Sheffield et al., they are on scales of tenths of PDSI units on continental-global scales. Big short term droughts, which are primarily driven by precip anomalies, will be captured by PDSI regardless of the method used to describe evapotranspiration. For that matter, the magnitude of long-term change looking forward, associated with really big century scale temperature change, will show up as ‘long term drought’ regardless of the details of the PDSI calculation. That’s why so many different hydrologic indicators (streamflow, vapor pressure deficit, etc.) that do not incorporate similar debatable ET parameterizations all point in the same direction. And that’s why I don’t think the Sheffield paper should require us to reject the validity of the core conclusions presented in so many recent papers.